Collagen fibres in otosclerosis and in osteogenesis imperfecta tarda. A light and electron microscopic study

Is it necessary to screen for hearing loss in the paediatric population with osteogenesis imperfecta?

The aim of the study was to assess the necessity of a screening service to detect early hearing loss in the paediatric population with osteogenesis imperfecta. Twenty-two children were assessed over a 5-year period. Five children (22.7%) had normal hearing. Fourteen (63.6%) had conductive hearing loss, with 12 children in this group having otitis media with effusion (OME); all had resolution of hearing loss with appropriate therapy. Two children had persistent conductive losses unrelated to OME. Three children (13.6%) had sensorineural hearing loss, with one being detected at the age of 1 year. Existing evidence suggests that hearing loss associated with osteogenesis imperfecta has its onset in the second to third decade of life. Contrary to this, hearing loss was detected in 77.3% (17) of this population with a median and mean age of 9 years. This study would suggest that routine screening is worthwhile in children with osteogenesis imperfecta.

Results of stapes surgery on patients with osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heterogeneous group of connective tissue disorders. The classic triad of blue sclerae, spontaneous fractures and hearing loss is known as the Van der Hoeve and De Kleyn syndrome. Between 1989 and 2000, six patients with OI presented with conductive hearing loss. Five of them proceeded to stapedotomy. All the patients who had surgery had significant hearing gain. None of the patients had any complications. This study presents a higher incidence of spontaneous fractured crura as the cause of the conductive hearing loss than previously reported, and that the presence of a fractured crura with mobile footplate can be anticipated by the presence of a large conductive hearing loss. The pre- and postoperative results are presented and support the view that stapes surgery in OI can have encouraging results, provided the operator anticipates the possibility of a fractured crura and a mobile footplate.

Scanning electron microscopy images and energy-dispersive X-ray microanalysis of the stapes in otosclerosis and Van der Hoeve syndrome

OBJECTIVE/HYPOTHESIS

The objective of this study was to evaluate the morphological and microchemical changes that affect sclerotic stapes in otospongiosis and van der Hoeve syndrome.

METHODS

A scanning electron microscope equipped with an energy-dispersive x-ray analyzer was used in the experiments.

RESULTS

In otosclerosis, focal lesions are poorly mineralized, with low calcium salt and reduced calcium-to-phosphorus (Ca/P) ratio (1.9:1). This finding correlates with a spongiotic type of lesion and indicates unstable mineralization with possible change from hydroxyapatite to calcium triphosphate. In van der Hoeve syndrome the presence of magnesium in stapes suggests osteoclastic function stimulation. The osteoclasts secrete many protons, causing an acidified microenvironment. Brushite is formed, and Ca/P ratio decreases in comparison with that of control patients (2.0:1 vs. 2.6:1).

A morphological and ultrastructural study of bone in osteogenesis imperfecta

A morphological and electron microscopic study of bone from patients with osteogenesis imperfecta (OI) has been performed. Bone from OI patients from various anatomical sites has been compared with that from normal, age-, site-, and sex-matched controls. The morphology of OI bone appeared variable among patients and sites of bone examined. Immature woven bone and a poor lamellar pattern were the significant morphological features and demonstrated that OI could not be characterized on the basis of a single histological pattern. At the ultrastructural level, a number of previously unreported features were evident. Abnormal collagen fibers and an altered mineral composition were found in many OI patients, however, the panoramic heterogeneity between clinical types and indeed within a single clinical type made it difficult to classify OI in this manner. The presence of intermitochondrial inclusions containing calcium and phosphorus and the presence of a stromal calcification in the bone in some OI patients suggested an abnormal mineral formation. Qualitatively, no obvious difference in the number of osteoblasts or osteoclasts was observed. The morphology and ultrastructure of OI bone were good indicators of the disease and serve a role in assessing the progress of a patient through diagnosis and treatment. This report presents new ultrastructural findings in collagen and in mineral formation in OI compared with normal human bone.

A morphometric analysis of osteoid collagen fibril diameter in osteogenesis imperfecta

Osteogenesis imperfecta is a genetic disorder of connective tissue characterised by frequent bone fracture following minimal trauma. Mutations of type I procollagen genes have been widely reported as the cause of OI and such mutations have been shown to introduce kinks into the collagen molecule. A study was performed to examine type I collagen fibrils at the ultrastructural level in the transmission electron microscope (TEM). Type I collagen fibrils from the bone osteoid of OI patients and age- and site-matched normal control bone were photographed in the electron microscope. A histomorphometric analysis of the diameters of collagen fibrils photographed in the TEM indicated that type I collagen in OI bone was larger in diameter compared with normal bone. This increase in diameter of type I collagen fibrils may represent an alteration in the quaternary structure of the collagen fibril as a consequence of kinked, poorly packed collagen molecules. Such alteration in the collagen fibrils may affect the formation and stability of bone mineral associated with it.

A clinical and audiological investigation of osteogenesis imperfecta

Fifty-six patients with osteogenesis imperfecta underwent clinical and audiological assessment. They completed questionnaires regarding their physical and otological disabilities, and attended various centres for audiological testing. It was found that 31 patients had a hearing loss. Hearing loss began in the second and third decades as a conductive loss, and progressed to a mixed loss. Eight patients, found in all age groups, had a pure sensorineural loss in one or both ears. Patients with osteogenesis imperfecta congenita suffered more fractures, became more physically disabled and had more severe hearing loss than those with osteogenesis imperfecta tarda. Tympanometry was found to give unpredictable results and was unhelpful in assessing middle ear function in these patients.

Pathology of otosclerosis: a review

Otosclerosis is a bone disorder of unknown etiology confined to the otic capsule. Failure of remodeling of newly formed vascular, woven bone (otospongiosis) results in sclerotic bone (otosclerosis) with abnormal osteons. Involvement of the oval window causes conductive hearing loss. Electron microscopic, histochemical, and biochemical studies identify normal cellular and matrix components of otosclerotic bone without providing clues to the abnormal bone formation and resorption. Plastic-embedded, nondecalcified histologic sections with in vivo tetracycline labels permit the study of mineralization rates to separate this disorder from other bone dyscrasias that have similar histopathologic appearances. Characterization of the cells, matrix, and their mediators can yield an understanding of abnormalities that disorder bone.